This project focuses on the establishment of a new class of natural proteins as therapeutics for treatment of cancers. Specific aims for the next period focus on providing a solid foundation for advancing a first-in-class biologic into human clinical trials for treatment of malignant melanoma. The application is based on the novel, expanded function of an activated form of a human tRNA synthetase and its applications to oncology. The synthetases (one for each amino acid) are ancient, universal proteins that catalyze attachment (aminoacylation) of each amino acid to its cognate tRNA in the first step of protein synthesis. We focused on the ex-translational function of a specific tRNA synthetase-tryptophanyl tRNA synthetase--where physiological relevance is clear. A naturally produced alternative form of human TrpRS, named as TrpRSAct, has potent anti-angiogenic activity through a mechanism that has been worked out in some detail. In particular, it blocks the assembly of new blood vessels and simultaneously inhibits activation of genes associated with angiogenesis. Because it inhibits new blood vessel formation, with no disruption of existing blood vessels, TrpRSAct has appeal for therapeutic applications to oncology. In addition to its strong anti-angiogenic properties, preliminary work showed that exogenously provided TrpRSAct activates destruction of a cellular protein that is involved in the etiology of many cancers, and is the target of new anti-cancer therapeutics. Preliminary work showed a strong therapeutic response to TrpRSAct when administered to mice bearing two different melanomas. The concepts and new treatments that emerge from this work are intended to change and expand the perspective and vision of investigators who focus on developing new approaches to cancer treatment. Specifically, while virtually all approaches to cancer therapies rely on small molecule chemotherapeutics or monoclonal antibodies, the proposed work introduces an entirely new first-in-class therapeutic protein. In addition, because the mechanism of action of TrpRSAct is distinct from those of the approved chemotherapeutics or monoclonal antibodies, it may be used in combination with existing therapeutics. Preliminary studies show strong activity of TrpRSAct when used alone, or in combination with a chemical agent. This success of the combination is doubtless because the mechanism of action of TrpRSAct is different. Thus, beyond the use by itself, TrpRSAct could lead to many new and expanded combination therapies.